DE2801820A1 - PROCESS FOR IMPROVING THE SOLUTION STATE OF VISCOSES - Google Patents

Description

2301820

In the known production of shaped structures, such as threads, fibers and foils, from regenerated cellulose the viscose process, it is of crucial importance for the economy of the process, the specific Reduce chemical consumption to a minimum. For example, there has been no shortage of attempts, so-called savings viscose to produce, i.e. spinnable solutions of alkali cellulose xanthate in dilute sodium hydroxide solution or water, in which the alkali ratio (ratio of the NaOH content on the cellulose content in percent by weight) has been reduced to values below 0.6 and, if necessary, additionally also the amount of carbon disulfide used was decreased.

The lowering of the alkali ratio (AV) of viscose has the consequence that not only the specific NaOH consumption but also the specific sulfuric acid consumption in the spinning bath system and the costs for the spinning bath regeneration and sodium sulphate discharge can be reduced. A lower use of carbon disulfide in relation to the use of cellulose or the amount of regenerated cellulose produced inevitably leads to an additional relief of the Exhaust air purification system.

Even in the production of viscose without compliance with saving conditions, the production of homogeneous spinning solutions is possible a problem, since it is stirred, pumped around or Grinding is not possible that; To convert cellulose xanthate quantitatively into the dissolved state. It remains rather, only to a small extent only swollen or partially dissolved slimy substances back that must be removed from the highly viscous solution by several successive filtrations before spinning. The state of the solution, i.e. essentially the filterability, of viscose is deteriorated, for example, by the lowering of the AV to such an extent that the

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Production of homogeneous / spinnable viscose is only possible with a filtration effort that is no longer justifiable is.

A lowering of the AV of viscose is largely only possible by lowering the NaOH content of the alkali cellulose, line Reduction of concentration or temperature increase of the immersion liquor used and the control of a higher one The degree of compression of the alkali cellulose inevitably leads to a poorer solution state for the viscose produced therefrom. It is possible that DT-OS 1 924 804 describes a process in which the NaOH content is reduced the alkali cellulose does not necessarily lead to a deterioration in the filterability of the viscose produced therefrom leads. However, this process works with a second alkalization after the pre-ripening and is therefore not only extraordinarily expensive due to the additional equipment required but also due to the additional energy requirement.

It has now been found, surprisingly, that it is possible using the usual alkalizing and suIfidizing devices To produce viscous and especially economical viscous from an excellent state of solution when the mashing of the alkali cellulose xanthate and / or the actual dissolving of this xanthate in dilute sodium hydroxide solution or Water is done under pressure. The overpressure should be about 1 to 30, preferably 2 to 15 bar. Particularly good ones Results were observed in the pressure range from 3.5 to 10 bar.

This pressure treatment should, if possible, be maintained during the entire mashing and dissolving process. This is e.g. possible in a simple way if the xanthate was produced in Baratten and then in separate viscose solvents is dissolved with sodium hydroxide solution or water while stirring and under simultaneous application of pressure.

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In some known viscose processes, the xanthate is already collected in the suIfidierapparaten, which are usually not equipped for a corresponding overpressure. In these cases it is advisable to use the mashed and possibly already partially dissolved xanthate Immediately after transfer to the dissolver or dissolver under pressure and simultaneous stirring, pumping if possible and / or attrition to further loosen. In general, it is important to have an overpressure during the time of mashing and / or dissolving

to maintain, while the still free, not bound to the cellulose carbon disulfide is present.

The generation of the upper pressure can be different, known Wise done. For example, on dissolving containers that have the form of autoclaves, nitrogen or another suitable gas or gas mixture are pressed. Corresponding what is effective is the generation of the pressure by suitable conveying devices, such as pumps.

The treatment time under pressure can vary depending on the start and level of the applied overpressure. For example, detectable improvement of the solution state so treated viscoses already at a pressure of, for example 10 bar observed after times of less than 1 minute, whereas at a pressure of only 2 bar corresponding changes in pressure treatment times of at least one minute detectable sine. ¹

The improvement found in the solubility of viscose increases with increasing pressure. Particularly good results were found with overpressure values of 3.5 to 10 bar and treatment times of 15 to 60 minutes. Through pressure increase over 10 bar beyond, e.g. to 30 bar, a further improvement in the state of the solution can be observed. But there at the same time with increasing pressure, the expenditure for the required apparatus increases, an increase over 30 bar appears

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2301820

... 5 -
Overpressure no longer makes sense.

A similar dependence was found for the treatment time. As already mentioned above, when high pressures are used, the dissolution of the xanthate is at an early stage A clear improving effect can be observed even at times of less than one minute. The improvement of the state of the solution can be further improved by extending the overpressure treatment. An extension over 180 minutes is easily possible, but the percentage improvement in the state of the solution is then only slight.

It has also been found that it is not necessary to start the dissolving process by always applying the same overpressure to improve. If required by the equipment, different Pressure values are applied, with higher pressure values preferably maintained at the beginning of the release process should be. If desired, it is also intermittent Pressure treatment of the viscose possible, i.e. that the viscose is only briefly exposed to pressure treatment, then is relaxed to normal pressure and then subjected to a pressure treatment, relaxation, pressure treatment, etc. again. Even with such a treatment, the total time of the pressure treatment should preferably be used during the dissolving process between one minute and 180 minutes, however, preferably between 15 and 60 minutes.

The described method for improving the solution state of viscose is not limited to the actual The solution process is limited in the case of low viscosity, but is also particularly suitable for the production of homogeneous, spinnable ones Viscose from poorly opened cellulose and to improve the solubility of viscose parts, whose state of solution was impaired by procedural errors.

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If poorly digested pulps are used, processing according to the method according to the invention is possible, if under normal conditions - but mostly not under economy conditions - alkalization and sulphidation are carried out and then the solution process is carried out according to the method according to the invention.

In the case of viscose parts that have a high number of swelling bodies and other slimy impurities / is even A subsequent improvement of the solution status is possible if, if necessary. addition of additional carbon disulfide, a new solution treatment according to the erfindutngsgemäße Process is carried out under positive pressure.

The effect of the process according to the invention is presumably based on a higher conversion of the carbon disulfide with the cellulose than in the previously known processes. As is well known, carbon disulfide does not only form a compound with cellulose in the form of xanthate in the viscose process. Rather, some of the carbon disulfide is subject to the known side reactions, for example the formation of sodium trietiocarbonate. For example, when sulfiding and dissolving at normal pressure by the usual method using 36 to 37% by weight of carbon disulfide based on the cellulose content of the alkali cellulose, only about 88% of the carbon disulfide used is bound to the cellulose. However, if one proceeds according to the invention and exposes the young viscose to a pressure of 7 bar, it is achieved that 96 % of the carbon disulfide used is bound to the cellulose after the dissolution process has ended. The carbon disulfide bound to the cellulose was determined according to Bredee, Colloid. Z · ¹ } A (1941), 85. Even with a subsequent addition of carbon disulfide, more xanthate groups are presumably formed, which promote the dissolution process.

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The filter clogging constant was used to characterize the state of the solution chosen. This constant was determined after

Hermans and Bredee, Rec. Trav. Chim. Pays-Bas 54 (1935), 680 ff. The viscose to be tested is introduced into a cylindrical steel vessel, as is described, for example, in "Götze, chemical fibers after the viscose process", third edition (1967), Volume II, 1115, FIG. 783 and filtered through 3 layers of cotton batiste (fabric setting; warp 52 threads / cm, weft 49 threads / cm, m ² weight 84 g / m ^{2) at a constant pressure of 2.0 atmospheres.} The effective filter area for this test filtration is 8.77 cm ² . The amount of filtrate that accumulates during the filtration time from 0 to 20 minutes (p ..) and in the filtration time from 20 to 60 minutes (p ₂ ) is measured. The clogging constant is then calculated using the formula

l - ^ K = 100,000 \ P1

W '

P _{2 +} P ₁

Comparisons with operational filtration showed that the following Assignment of the measured K values is possible.

Vr

K value Assessment of filterability

<300 very good

300 - 500 good

500 - 800 difficult

800 - 1,000 bad

"^ 1,000 practically no longer filterable.

The following are intended to further illustrate the invention Examples serve. In some cases, special information about the analytical methods used was dispensed with, as these For example, in the cited monograph by Götze, op. cit., Volume 2, Chapters 42 and 43 have been described in detail. Unless otherwise noted, amounts and percentages relate to amounts by weight.

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2 - μ 1 B 2

ο

A beech sulphite pulp with a CK -CcI Ij ]ose content of 91.2% and an average polymerisation rate (DP) of 820 was used as the starting point for a series of experiments. The DP was determined in all areas by means of emulsion xanthogenation according to Jayme -Wellm, Das Papier Y \ _ (1957), 77-82.

In each case, sheets dos pulp immersed in a Alkalisierpresse the company Blaschke, Enders Bach, the dipping time was 30 minutes at 5 ^r 5 ° C. An immersion liquor with 190 g / l NaOH and 10 g / l hemicellulose was used. After pressing an alkali cellulose, and shredding the cellulosic i 35.0 and 14.0 'i NaOH was each obtained contained. During the subsequent preripening the alkali cellulose at 55 ° C and a Vorreifczoit of ^, ^r> hours, the DP was lowered to 305th The sulfidation took place in evacuated containers for 90 minutes at 30 ^° C. The η carbon disulfide amounts used varied between 34 and 37 r. They are listed in the table below.

The xanthates obtained in this way were subjected to different dissolution conditions. In each case, water and dilute sodium hydroxide solution were added in such an amount that the cellulose content of the viscose produced was 9.0% , while the content of NaOH and thus the alcohol ratio (^ V) of the viscose was varied.

Dissolution process according to the state of the art.

The solution was dissolved in open containers, once using a propeller stirrer operated at 1,370 rpm. the Treatment time was 2.5 and 5 hours, respectively. Furthermore, viscose became the effect of a for a period of 5 hours Attritor (Condux disk mill) exposed.

Dissolving according to the method according to the invention.

Again, two different procedures were used. Once

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the loosening was done starting with; oem Λΐιπ'α i acl .'- n in an autoclave with a long: ■; ■ "<in 1 ..uf >> pdi η 'f,; n ·!]. ·> ι iiiit .. -rk (r-tv / 100 U / min.) ciusgo was allowed. After d ^ r "u'f.ibe <\ äo <; required
Water and the diluted sodium bicarbonate nitrogen was pressed into the autoclave. During the g ·.; £ ·> ■ ".mt on solving process of
2.5 hours, a pressure of 7 bar iu ί recii ί ^'s rha it en.
In a further series of tests, 7LmMcP-Ht was ah
A gear pump pressed into a container that had an overflow valve that was set to 2 bar overpressure.
The viscose emerging from this valve ran into the. pressureless mashing tank and got back into the pressure film with the help of the gear pump. The C: .- aanit dissolution time in this case was also 2.5 hours, with the viscose medium being exposed to an overpressure of 2 bar for a total of 25 minutes.
The different procedural conditions μ π as well as? the obtained measured values of the FiI tervorstopi "ungskonstan Le K, ΗΪίκι in the
table below.

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Λ Ika1Lverh.
il. Visose

Cf: .j j Pil t ervorstopf uii ■ (. K ^ nr: t ar.t cn K, "I hf i vi T; I i e that. Ι, ό.; ·. BcdinauiKjon

^r ose time while stirring

while stirring

, 55 3 7 1. 800 6.0 O , 15 3 7 3. «J 50 690 O , 40 37 160 820 O , 40 34 400 1,800 O

>> yi-i.
with Ze.r-

6 40

30 5

.655

2.5 Jt cl.

Loose time pressure after gear

420 280 4 25 310 435 320 610 330

2, Si! Tr release time in the autoclave

7 bar

From the measured values of the table is oir.ueutiq be seen that the Λην / endunq a · -. Pressure during dos Anmaischens and / or l.öseiis tjon.aß the vet lit'qcM.den f.'rf liit'unq :: u leads to a significant improvement in the solution. In particular, it is possible to dispense viscose under reduced conditions. oils that still show good filterability.

BeJ-spjej. 2:

Under the same alkalizing, preliminary rolling and sulfiding conditions As in example 1: - · * Buchr-nyul f i t cellulose with untorschiedl ichei ,; cL-Cel lulo: "egeha Lt and ash content Alkn1icellulose-Xanthoqenate produced, which then again under different conditions were adjusted and resolved. The following cells were used

Designation of the pulp CX -cellulose content " Ashes ϊ,

l \

0.054

B C

9 0.3 37.8 0.11 0.16

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The xanthates obtained were dissolved with the calculated amount of water and dilute sodium powder in an open container using a propeller belt (approx. 1,370 rpm) for a period of 2.5 hours. In a parallel experimental series, the mashing and dissolving in an autoclave with a slow speed stirrer (ca 100 U / min) carried out ort ind'ingsaomäß, wherein during the entire Anmaisch- and dissolving time of 2.5 hours, a pressure of 9 bar by pressing was maintained by compressed air.

In a third series of experiments, the xanthate was seen annually under formal pressure and with the aid of a propeller stirrer. The mashed xanthate was then immediately conveyed with the aid of a gear pump into a room in which an overpressure of 9 bar was maintained with the aid of a pressure holding valve. The size of this pressure space was designed so that only part of the total amount of viscose could be absorbed. Therefore, the young viscose remained some time in the pressure chamber and then flowed through the pressure holding valve back into the non-pressurized storage tank of the gear pump back _ui: Then again supported by the gear pump into the container :: ■ ·: graze. The total dissolution time in this series of tests was 2.5 hours, but the total residence time of the viscose under a pressure of 9 bar was only 19 minutes on average.

In each case, viscose was produced using 37 % carbon disulfide and an alkali ratio of 0.6. The cellulose concentration of the viscose was 9.0 % in each case.

The determination of the filter clogging constant was again used to characterize the state of solution of the various viscoses Kw. The values obtained have been compiled below.

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Pulp filter clogging constant Kw according to

2.5 hours 2.5 hours 2.5 hours

Release time Release time Release time in

with stirring pressure after autoclave

Gear pump

9 bar 9 bar

A 450 180 170

B 1,210 360 280

C 1,620 385 305

The viscose produced from the pulp C with stirring at normal pressure for 2.5 hours was then placed in an autoclave redissolved at 9 bar overpressure for 2.5 hours. By this measure could still significantly affect the solution state

be improved. The viscose treated in this way showed a filter clogging constant Kw of after dissolving 370. However, such a viscose was made with an additional amount of 2.0% carbon disulfide, based on the cellulose content the viscose, added and then a corresponding subsequent solution in the autoclave at an excess pressure of 9 bar exposed for 2.5 hours, the state of the solution further improved. The filter pulp constant Kw was then only 195.

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Claims (4)

HOECHST AKTIENGESELLSCHAFT file number: HOE 78 / P 000 Date: 16.O1.1978 Dr.FK/wö Process for improving the solution state of viscose Patent claims: 1. Process to improve the solubility of viscose, "characterized in that the mashing of the alkali cellulose xanthate with dilute sodium hydroxide solution or water and / or the dissolving of the xanthate by stirring, grinding, pumping or the like.
takes place at an overpressure of about 1 to 30 bar. 2. The method according to claim 1, characterized in that the overpressure is 2 to 15, preferably 3.5 to 10 bar. 3. The method according to claim 1 or 2, characterized in that the pressure treatment as possible immediately after mashing of the xanthate begins and lasts about 1 to 180 minutes, preferably 15 to 60 minutes. 4. The method according to claim 1, characterized in that viscose of poor solution state after adding additional Carbon disulfide redissolving by pumping, stirring, grinding or the like at an overpressure from 1 to 30 bar. 909829/0396